Help: How to Count number of lines in JAVA?

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1.00/5 (2 votes)

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Hello there fellow programmers, I have a question: Write a static method, Display() that accepts a string representing the name of the file. The method should read and display only the first the five lines of the file's contents. If the file contains less than 5 lines, it should display the file's entire contents.

(Assuming that I made all the necessary imports) Here is my attempt:

public static void Display (String filename) throws IOException
{
   File file = new File (filename);
   Scanner read = new Scanner (file);

   while (read.hasNext())
   {
//So far I have tried this
       int count=0;
       String lineReader = read.nextLine();
       count++;

      if (count <5)
      {
        System.out.println(lineReader);
      }
   }
   
   read.close();

}

Posted 18-Apr-13 10:22am

fatand50

Updated 18-Apr-13 11:02am

v5

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Sergey Alexandrovich Kryukov 18-Apr-13 16:25pm

OK, and where is your question? :-)
—SA

fatand50 18-Apr-13 16:28pm

It's on top before the code. But here it is:
Write a static method, Display() that accepts a string representing the name of the file. The method should read and display only the first the five lines of the file's contents. If the file contains less than 5 lines, it should display the file's entire contents.

Richard C Bishop 18-Apr-13 16:33pm

That reads a lot like a homework assignment.

Sergey Alexandrovich Kryukov 18-Apr-13 16:35pm

I answered the way not giving out all the "secrets". It's good to do by OP's own hands.
—SA

Richard C Bishop 18-Apr-13 16:38pm

Nice work.

Sergey Alexandrovich Kryukov 18-Apr-13 16:45pm

Thank you,
—SA

fatand50 18-Apr-13 16:42pm

Okay let me try. Thank you.

Sergey Alexandrovich Kryukov 18-Apr-13 16:45pm

Good idea. Will you accept the answer formally (green button)?
—SA

Sergey Alexandrovich Kryukov 18-Apr-13 16:34pm

Thank you. But what's the problem?
—SA

José Amílcar Casimiro 18-Apr-13 16:28pm

count the lines you're reading and change the loop condition to achieve your goal.

fatand50 18-Apr-13 16:30pm

Yes but how? That is the part I don't know or that I've never encountered. I really need to know how to do this.

DinoRondelly 18-Apr-13 16:34pm

You need to play around with this and try you will find it isnt as hard as you think it is. No effort no reward ...

Sergey Alexandrovich Kryukov 18-Apr-13 16:35pm

Good idea. I provided only a hint-type answer.
—SA

fatand50 18-Apr-13 17:03pm

Sorry Sir, What is a over-kill?

Sergey Alexandrovich Kryukov 18-Apr-13 17:09pm

Or, this the idiom of English jargon we often use...

Let's say, you killed a person. If you want to kill the same person again ("overkill"), this person won't be more dead then before, right?
So, this idiom is used to note that some strong and potentially overly complex or heavy-weight tool can be inadequate to solve a problem which can be perfectly solved by much weaker/simpler/light-weight tool.

The problem of text parsing is by far more difficult than the problem of counting lines or sequentially reading of all the lines...
Did I explain it now? clear enough?
—SA

fatand50 18-Apr-13 17:13pm

I now understand, thank you Sir. I can count the number of lines by printing the count but do not know how to validate :(

Sergey Alexandrovich Kryukov 18-Apr-13 17:15pm

I have no idea what needs validation. You did not mention anything like that before.
—SA

José Amílcar Casimiro 18-Apr-13 17:30pm

In my country [PT] there is an expression: "use a cannon to kill a fly." :-)

Sergey Alexandrovich Kryukov 18-Apr-13 17:48pm

Sure. In my country we say "shooting from a cannon on sparrows"...
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-04-18T10:32:00

Solution 1

Using java.util.Scanner just for counting lines is a big overkill! However, you are close. Declare some integer counter variable, initialize to 0 before the loop and increment each time you successfully find next line.

Without such an overkill, use java.io.BufferedReader and java.io.BufferedReader.readLine:
http://docs.oracle.com/javase/1.5.0/docs/api/java/io/BufferedReader.html[^],
http://docs.oracle.com/javase/1.5.0/docs/api/java/io/BufferedReader.html#readLine%28%29[^].

—SA

Posted 18-Apr-13 10:32am

Sergey Alexandrovich Kryukov

Updated 18-Apr-13 10:33am

v2

Comments

DinoRondelly 18-Apr-13 16:39pm

+5, more then i would have given for this question, OP should learn something with this answer.

Sergey Alexandrovich Kryukov 18-Apr-13 16:44pm

Thank you, Dino.
—SA

Espen Harlinn 18-Apr-13 17:01pm

5'ed!

Sergey Alexandrovich Kryukov 18-Apr-13 17:12pm

Thank you, Espen.
—SA

fatand50 · Accepted Answer · 2013-04-21T01:34:00

Java

public static void Display (String filename) throws IOException
{ 

   int lineCounter=1;

   File file = new File (filename);
   Scanner read = new Scanner (file);
 
   while (read.hasNext() && lineCounter<=5 )
   {

       String lineReader = read.nextLine();
        System.out.println(lineReader);
        lineCounter++;
      
   }
   
   read.close();
 
}

[edit]Code block added[/edit]